Well, going on research run by a government council rather than a PA firm for a supermarket or retailer...
http://www.leicester.gov.uk/news/news-story-details?nId=81297
Removed actual figure so that people can guess before clicking through.
Hm, that is interesting but addresses the opposite of mass products: locally produced and labelled meat products. For those my estimates would look much different.
Press Release
Edit: Soylent's Reply, provided by Trevor_Blake